1. Field of Invention
This invention relates to emergency coolers having large pools of quiescent liquid suceptible to rapid boiling away to cool an unscheduled emergency surge of heat. Some embodiments of this invention are flame arrestors for gas pipelines. This invention concerns protecting the entry portion of tubes of a heat exchanger from over-heating, while still cooling the flowing stream about half as much as without such protection.
2. Prior Art
Many tons of compressed ethylene have been transported over long distances by pipeline, notwithstanding the recognition that compressed ethylene does not have the same safety characteristics as compressed methane. As noted in the three ancestral applications referred to, it has been recently discovered that a flame arrestor having megawatt cooling capacity can quench a decomposition flame even though the flame front can have a temperature such as 3000.degree. F. Some of the engineering work relating to such flame arrestor assumed that the heat transfer tubes would be of stainless steel, thereby being capable of withstanding satisfactorily an elevated temperature. The economic advantage of using conventional alloys instead of stainless steel was recognized initially, but the 3000.degree. F. temperature of an ethylene decomposition flame provided justification for stainless steel.
Stephenson, U.S. Pat. No. 2,087,170 explains that check valves of a hydraulic nature have been employed as flame arrestors and proposes alternative flame arrestors for systems using acetylene at slight pressure. Although apparently aimed primarily at backfiring of combustible flames, Stephenson mentions caloric waves arising from the decomposition of acetylene. The flame front for the decomposition of acetylene is now known to migrate at a speed which is orders of magnitude faster than an ethylene decomposition flame front. Moreover, because acetylene is ordinarily compressed only to a slight pressure, the heat content per volume of acetylene decomposition is much lower than the heat content for the same volume of highly compressed ethylene. Stephenson, U.S. Pat No. 2,087,170 discloses a shell through which water is circulated to cool tubes in the very short flame arresting zone. Compressed acetylene ordinarily is piped only a short distance, whereas ethylene is sent by gas pipelines for significant distances, such as greater than a kilometer. Said Stephenson patent provided meagre guidance to ethylene technologists.
Heat exchangers for sulfur burners are designed for continuous, reasonably uniform heat content of the gas stream directed to the heat exchanger, and are also designed for the circulation of cooling liquid. In order to overcome some corrosion problems in such heat exchangers, ceramic insulating ferrules have been inserted at the entry portion of each tube and have extended for a few inches into the tube. Such ceramic ferrules protect the heat transfer tubes and help to overcome certain corrosion problems tending to occur at the point of joining of the tube and the tube sheet. The ceramic ferrules have been sensitive to thermal shock and have had propensities to spall and/or crack when rapid changes of temperature were encountered, but have served to protect against corrosion problems under uniform heat transfer conditions.
Notwithstanding the well-recognized cost advantage of using conventional steels when feasible, the use of stainless steel in a flame arrestor for an ethylene pipeline was deemed appropriate over a period of many months of design of such devices.